Multi-source plasma focused ion beam system

ABSTRACT

The present invention provides a plasma ion beam system that includes multiple gas sources and that can be used for performing multiple operations using different ion species to create or alter submicron features of a work piece. The system preferably uses an inductively coupled, magnetically enhanced ion beam source, suitable in conjunction with probe-forming optics sources to produce ion beams of a wide variety of ions without substantial kinetic energy oscillations induced by the source, thereby permitting formation of a high resolution beam.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to the field of ion beam systems.

BACKGROUND OF THE INVENTION

A typical focused ion beam (FIB) system using a gallium liquid metal ionsource (LMIS) can provide five to seven nanometers of lateralresolution. Such systems are widely used in the characterization andtreatment of materials on microscopic to nanoscopic scales. A galliumLMIS typically comprises a pointed needle coated with a layer ofgallium. The needle may be maintained at a high temperature while anelectric field is applied to extract ions from the source.

FIB systems with gallium LMIS's are used in many applications because oftheir ability to image, mill, deposit, and analyze with great precision.Milling or micromachining involves the removal of bulk material at ornear the surface. Milling can be performed without an etch-assistinggas, in a process called sputtering, or using an etch-assisting gas, ina process referred to as chemically-assisted ion beam etching. U.S. Pat.No. 5,188,705, which is assigned to the assignee of the presentinvention, describes a chemically-assisted ion beam etching process. Inchemically-assisted ion beam etching, an etch-enhancing gas reacts inthe presence of the ion beam to combine with the surface material toform volatile compounds. In FIB deposition, a precursor gas, such as anorganometallic compound, decomposes in the presence of the ion beam todeposit material onto the target surface.

In ion beam-assisted deposition and etching, a gas is adsorbed onto thespecimen surface and reacts in the presence of the ion beam. The rate ofmaterial removal or deposition depends on the number of ions strikingthe target surface, the rate at which gas molecules are adsorbed by thesurface, and the number of atoms removed or deposited by each ion.

In all of the processes described above, the function of the galliumions in the beam is to provide energy, either to displace particles onthe work piece in sputtering or to activate a chemical reaction of amolecule adhered to the surface. The gallium itself does not typicallyparticipate in the reaction. Gallium is used in the beam because itsproperties, such as melting point, ionization energy, and mass, make itsuitable to form into a narrow beam to interact with commonly used workpiece materials.

There are disadvantages to using LMIS'S. With regard tochemically-assisted etching or deposition, because the gallium itselfmerely provides energy for the reaction and does not otherwiseparticipate, the reaction rate is limited by adsorption rate of thereacting molecules. For example, in FIB deposition, if the ion beamdwells too long at a point, the adsorbed gas molecules are alldecomposed and the beam begins to etch, rather than deposit. To mill ordeposit, the ion beam is typically scanned repeatedly over a rectanglein a raster pattern. As the beam completes a scan, the beam is typicallydelayed for a significant amount of time before beginning the next scanto provide time for additional gas molecules to adsorb onto the surfacebefore beginning a new raster. This increases processing time.

Moreover, gallium atoms implant into the work piece and, in manyapplications, produce undesirable side effects, such as changing theopacity or electrical properties of a work piece. Gallium can alsodisrupt the crystal structure in the area of bombardment. The type ofion emitted from a LMIS cannot be readily changed, which is adisadvantage because different ion species may be preferred fordifferent processes. To change the ion species, the source must beremoved from the vacuum chamber and replaced with a different source,which must then undergo a time consuming preparation procedure. Also, toproduce a very narrow beam, the current in a beam from an LMIS must bekept relatively low, which means low etch rates and longer processingtimes.

Plasma etch systems used in semiconductor manufacturing, unlike beams ofgallium atoms, typically use ions in a plasma to chemically react withthe work piece. Such systems, however, typically provide a reactiveplasma over the entire surface of a wafer and are not used to locallyetch or deposit fine features.

Plasma ion sources have been used to form ion beams, but such beams arenot typically used to mill or deposit fine features on a work piecebecause beams from plasma ion sources were difficult to focus into afine spot while maintaining a useful beam current. Such beams weretypically used either to broadly etch a large area, such as to thinsamples for viewing on a transmission electron microscope, or to producea small spot size at low beam current, for example, for secondary ionmass spectroscopy analysis. Moreover, such plasma sources are limited tothe specific types of gases and the lifetime of such sources arerelatively short with some gases because the plasma would corrode thecathode.

The magnetically enhanced, inductively coupled plasma ion sourcedescribed in U.S. Pat. Appl. Publ. No. 2005/0183667 for a “Magneticallyenhanced, inductively coupled plasma source for a focused ion beamsystem” can be used to produce a finely focused beam with a relativelylarge beam current, thereby overcoming many of the problems of a galliumLMIS system. U.S. Pat. Appl. Publ. No. 2005/0183667 describes a systemusing a single ion species.

There is a need for a system that enables the user to selectivelyprovide gases of different ion species for performing differenttreatments of a specimen such as milling, etching, deposition andimaging, without requiring replacing the source.

SUMMARY OF THE INVENTION

Embodiments of the invention provide a method and apparatus forperforming multiple charged particle beam operations on a work piece andprovide for the use of different types of charged particles to operateon a work piece in a single system. The invention facilitatessequentially or simultaneously using different ion species to performvarious processes on a work piece. The different processes can beperformed with the most appropriate charged particle species for thatparticular process.

For example, an inert ion specie can be used to sputter or to activatean etch-enhancing gas or a deposition precursor gas adsorbed onto thesubstrate. In another example, the charged particle beam itself mayinclude an etch-enhancing gas or a deposition precursor gas, therebyeliminating the necessity of using a beam of one species to provide theactivation energy for a compound introduced through a gas injectionsystem. In yet another example, the beam species can comprise a materialto be directly deposited.

A preferred system uses a magnetically enhanced, inductively coupledplasma ion source, which provides a high brightness beam that can befocused onto a small spot and that can provide beams of a wide varietyof ion species by inputting different gases into the source.

The foregoing has rather broadly outlined some features and technicaladvantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter. It should be appreciated by those skilled in the art thatthe conception and specific embodiment disclosed herein may be readilyutilized as a basis for modifying or designing other structures forcarrying out many useful purposes of the present invention. It shouldalso be realized by those skilled in the art that such equivalentconstructions do not depart from the spirit and scope of the inventionas set forth in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1A shows a simplified schematic diagram of a multi-source,RF-excited, plasma ion chamber.

FIG. 1B shows an embodiment of an RF-excited ion plasma source.

FIG. 2 shows a circuit for adjustment of power transfer to the plasma.

FIG. 3 shows an embodiment of a focused ion beam system.

FIG. 3B shows a graph of performance of both a LMIS and a magneticallyinduced plasma ion source

FIG. 4 shows a flow chart of an embodiment of a process for milling anddeposition using a multi-source, magnetically induced ion beam system.

FIG. 5 shows a flow chart of an embodiment of a process for milling anddeposition using an organometallic ion species.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following is a detailed description of example embodiments of theinvention depicted in the accompanying drawings. The example embodimentsare in such detail as to clearly communicate the invention. However, theamount of detail offered is not intended to limit the anticipatedvariations of embodiments; on the contrary, the intention is to coverall modifications, equivalents, and alternatives falling within thespirit and scope of the present invention as defined by the appendedclaims. The detailed descriptions below are designed to make suchembodiments obvious to a person of ordinary skill in the art.

Embodiments of the invention provide for processing of submicronfeatures using charged particle beams. In a preferred embodiment, a workpiece can be sequentially processed with relatively high current usingsubmicron beams of different ion species, without removing the workpiece from the vacuum chamber and without having to change the ionsource, that is, the plasma chamber. The ion specie is changed byfeeding different gases into the ion source. Preferred embodiments canprovide a wide range of ion species for different types of processing.For example, an inert ion, such as xenon or helium, can be used tosputter or to activate an etch-enhancing gas, such as iodine, chlorine,or xenon difluoride, the etch-enhancing gas typically being introducedinto the vacuum chamber by a gas injection system separate from the ionbeam source.

An inert ion specie can also be used to activate a deposition precursorgas that decomposes in the presence of the ion beam to deposit amaterial, such as a conductor or an insulator, onto the work piece.Using an inert ion specie can eliminate contamination caused byimplanting the ions into the deposited material and the work piece. Manydeposition precursor gases are known, including tetramethylorthosilane(TMOS), tetraethylorthosilane (TEOS), tetrabutoxysilane Si(OC₄H₉),tungsten hexafluoride (WF₆), organometallic compounds, such as tungstenhexacarbonyl (W(CO)₆) and C₇H₁₇Pt.

Embodiments can also feed an etch-enhancing gas or a depositionprecursor gas, such as those described above, into the ion source toform the beam, alone or in combination with other gases, such as inertgases. Using an etch-enhancing gas or a deposition precursor gas as anion specie in the beam eliminates the necessity of introducing one gasthrough a gas injection system and eliminates the problem of theexhaustion of adsorbed gas molecules by the ion beam.

Embodiments can also use an ion specie in the beam that comprises thematerial to be deposited, analogous to spray painting the work piecewith the material in the beam. For example, a beam of carbon 60 (C₆₀)can be used to deposit carbon, to make a portion of photolithographymask opaque or to provide a protective layer on a surface. The ion beamcould also include mixtures of different species. For example, ametallic deposition precursor gas and an insulator precursor gas sourcecan be used together, to provide a beam that deposits a high resistivitymaterial, such as that described in U.S. Pat. No. 6,838,380, to Bassomet al. for “Fabrication of High Resistivity Structures using Focused IonBeams,” which is assigned to the assignee of the present invention.

The present invention facilitates multi-step processing by allowing theion species to be changed without having to remove the ion source,expose the vacuum chamber to atmosphere, and reinstall a new ion source.Thus, for example, the system can be used to sequentially, etch, image,deposit, image and etch. These steps can be performed in any preferredorder. The ion species can be changed by simply switching the gas inputinto the ion source. A vacuum pump can exhaust the remaining amounts ofthe previous ion species in the plasma chamber and the sample chamber.In preferred embodiments, the work piece can remain in the samplechamber for multiple processing steps using different ion species. Someembodiments will also permit electron beam processing, for example, forelectron microscopy, e-beam assisted etching, or e-beam assisteddeposition.

Multi-step processes may involve, for example, coating a material with aprotective or conductive layer using a first inert ion species togetherwith a precursor gas delivered through a gas injection system or in thebeam, milling a trench in the work piece using a second, heavier inertion specie together with an etch-enhancing gas introduced using a gasinjection system or in the beam to expose a cross section, and thenusing a beam of light inert atoms or electrons to form an image of theexposed cross section using scanning ion microscopy. A heavier inert ionspecie can be used in the beam to sputter the surface to performsecondary ion mass spectroscopy to determine the surface composition.

In accordance with one preferred method of the invention, an RF-excited,impedance-matched plasma chamber receives a gas from one or more ofmultiple available gas sources, and extracts an ion beam from thechamber. Ions can also be implanted into a substrate to charge itselectrical properties using gases such as AsH₃, PH₃ and BF₃. The methodfurther comprises introducing and ionizing a first gas for performing afirst operation and performing the first operation with a beam formed ofionized particles of the first gas. Then, a chamber holding the specimenis substantially evacuated of the first gas and ionized particles and asecond gas for a second operation is introduced and ionized.

Another embodiment comprises providing a plurality of different gassources to be selectively coupled to a plasma chamber. One of aplurality of source gases is selectively coupled to the plasma chamberfor a first process, and then, for a subsequent process, another gas isselectively coupled to the plasma chamber. A radio frequency (RF) sourceis applied to an antenna that couples energy to the selected gas withinthe chamber to induce ionization of the gas to produce an ion plasma.Circuitry is provided that couples the RF source to the antenna toreduce modulation of a plasma potential. An extraction mechanismextracts an ionized beam from a region of extraction in proximity to theantenna.

Another embodiment is an ion beam system for treatment of a work pieceusing beams containing different ions. The embodiment comprises a gascoupled to an electromagnetic field from a helical antenna positionedaround the plasma chamber and excited to ionize the gas within theplasma chamber. Circuitry in a network comprising the antenna impedancematches a source of excitation to the antenna. An extraction mechanismextracts an ionized beam to be directed onto a specimen. A first gas isselectively fed into the ion chamber for a first processing operation,and than a second gas is selectively fed into the ion chamber for asecond operation.

Preferred embodiments of the present invention include a multi-source,inductively coupled, magnetically enhanced ion beam source, suitable tobe used in conjunction with probe-forming optics to produce ion beamswithout substantial kinetic energy oscillations induced by the source.One of many advantages of the use of an inductively coupled,magnetically enhanced ion beam source, suitable to be used inconjunction with probe-forming optics is the ability to apply differention species for different purposes, without having to remove the samplefrom the vacuum chamber and without having to replace the ion source.Another of the many advantages is the relatively long lifetime of theinventive apparatus, in comparison to cathode sources for ionization ofa gas.

Another advantage of some embodiments of the invention is the fastdeposition rates that can be achieved using different ion species fordirect deposition in contrast to using a beam to merely induce reactionof precursor gases introduced into the sample vacuum chamber through agas injection system. Another advantage of some embodiments of theinvention is the high deposition rates or etch rates that can beachieved using precursor gases or etch enhancing gases in the ion beamitself in contrast to introducing precursor gases or etch enhancinggases into the sample vacuum chamber through a gas injection system.Another advantage of some embodiments of the invention is the reductionor elimination of contamination when using a beam of inert ions, asoppose to metal ions, together with a precursor gas or etch-enhancinggas introduced through a gas injection system. Another advantage of someembodiments of the invention is the ability to select an ion specie ofan appropriate mass for processing, such as a relatively heavy specieswhen it is desired to eject material near a work piece surface, or alighter ion when it is desirable that the beam penetrate further intothe work piece. Other advantages will be apparent from the followingdescription.

In various embodiments, the processing operations may include, forexample, deposition, milling, imaging, analyzing, implanting, or otheroperations. The beam can be composed, for example, of ions that interactchemically with the work piece material, ions that provide energy tosputter or induce chemical reactions, or both. As used herein, “a gas”may include a mixture of different compounds and is not limited to asingle molecular or atomic species. The ion beam can include, forexample, combinations of inert ions, precursors that decompose todeposit material, material to be directly deposited, reactive materialsthat combine with the work piece surface materials to form volatilecompounds that are removed from the system by the vacuum pump, reactivematerials that combine with the work piece surface materials to formnon-volatile compounds, such as oxides or nitrides, that remain on thesurface, or other ions.

FIG. 1A shows a simplified schematic diagram of a multi-source, RFexcited, plasma ion chamber. A ceramic plasma ion chamber 100 is wrappedby a coil 102. The coil is excited by an RF source, (not shown in FIG.1A). Ceramic plasma ion chamber 100 is a cylinder with apertureelectrodes 104 at one end. The aperture electrodes 104 exhibit anaperture centered on the cylinder axis of ceramic plasma ion chamber100. An ion beam leaves ceramic plasma ion chamber 100 through theaperture of the electrodes 104 and passes through an ion beam focusingcolumn 106 to produce a deflectable focused ion beam 108.

Ceramic plasma ion chamber 100 receives through a valve 109, gas fromone or more of a plurality of sources 110, 112, 114. Sources maycomprise inert gases such as xenon (Xe) or helium (He), reactive gasessuch as oxygen (O₂), or precursor or etch-enhancing gases as describedabove. Valve 109 may be provided to select in sequence or in combinationeach of a plurality of different gases from the sources. Thus, one maychoose one ion species for milling or etching and choose a seconddifferent ion species for deposition.

For example, one may first introduce a gas such as Xe for sputtering.The Xe gas is ionized in ceramic plasma ion chamber 100 and an ionizedXe beam is formed. Sputtering occurs as the ionized Xe atoms collidewith the substrate to be milled. After milling is completed, the plasmachamber may be evacuated. Then, one may introduce into the samplechamber through a gas injection system a flow of an etch-enhancing gassuch as Xenon Di Fluoride (XeF₂) and provide to the plasma chamber alight inert element such as He. Etch enhancing gases are typicallyselective, and may increase the etch rate of some materials whiledecreasing the etch rate of others. The He gas is ionized in ceramicplasma ion chamber 100 and an ionized He beam is formed. The ionized Heatoms bombard the molecules adsorbed to the surface to separate the Xefrom the fluorine (F) atoms. At the substrate, where the ionized heliumbeam strikes the surface of the substrate, dissociated fluorine atomsbond with silicon (Si) atoms of the substrate to form volatile SiF. TheSi atoms that bond with the F atoms leave the surface of the substrate.Thus, the substrate is chemically etched where it is impinged upon bythe ionized He beam. The Xe and SiF gasses are evacuated from thechamber. Thus, some embodiments provide a multi-step process to providedifferent successive treatments of a work piece. For example, in a firststep, a first ionizable gas can be introduced for sputtering and in asecond step a second ionizable gas can be introduced for etching ordeposition.

There are advantages to using an ionizable gas such as Xe for milling ascompared to using a LMIS providing an element such as gallium (Ga).Suppose, for example, one desires to mill quartz glass to form anoptically transmissive mask. Using a Ga LMIS for milling, some Ga atomswill embed in the quartz and undesirably disturb the opticaltransmissivity of the glass. In contrast, when using a heavy,non-reactive gas such as Xe, the ions do not remain in the quartz and anamorphous layer is formed at the surface of the quartz that is opticallytransmissive. Another disadvantage of an LMIS, in contrast to thepresent invention, is the inability to change ion species.

Use of an ion source that is excited by an RF field is preferable to anion source that relies on cathode emission to produce electrons thationize the gas. In a cathode-anode system some of the positive-ionizedgas atoms collide with the cathode and sputter it. Also, use of areactive gas results in deterioration of the cathode. This results in arelatively short lifetime for the cathode. In contrast, an RF excitedsystem according to embodiments described herein has no cathode. Rather,free electrons are produced by applying a time-varying voltage to anaperture electrode. Due to the RF field produced by the coil around theplasma chamber, these free electrons travel circumferentially in theplasma chamber. The free electrons bombard other gas molecules toproduce more ionized atoms. This in turn produces a plasma of very highion density. Moreover, the beam can be focused to a submicronGaussian-shaped spot or into a non-Gaussian shape, such as a rectangle,using known beam shaping techniques.

Thus, embodiments combine multiple gas sources, with RF plasma inductionto offer an additional degree of freedom for milling, deposition,imaging, analysis, and other applications. The gas sources may comprisesingle atom species, molecules or gas mixtures. For insulatordeposition, for example, to produce a layer of high resistivity, anoxygen primary ion species can be used to react with the work piecesurface material to form an oxide material, such as silicon dioxide or alarge ion such as Xe could be used with an appropriate precursor gas,such as TEOS or TMOS to deposit gallium free oxide that provides greaterresistivity that an oxide layer having implanted gallium from a galliumbeam. For quartz deposition, for example, to achieve high opticaltransmissivity, an inert or oxygen and silicon compound primary ionspecies may be used.

For minimal damage to a substrate, for example in a photo-resistapplication, one might use a low mass primary ion such as He to produceminimal sputtering and high secondary electron yield. As anotherexample, with carbon 60 (C₆₀) (or other structures, such as C₇₀, C₇₆,and C₈₄) as the primary ion type, one may perform direct carbondeposition without need for naphthalene. Applying carbon using C₆₀ isanalogous to spray painting the carbon onto the work piece.

Enhanced deposition and milling rates may be achieved with XeF₂ or SF₆plasma gases. Presumably, either of these gases flooded onto the samplewill result in etch enhancement. Gains in deposition rates might also beachieved due to higher secondary electron yield of a fluorinatedsurface. In short, embodiments allow the user to choose the primary ionspecies with the best combination of factors such as: secondary electronyield, ion mass, secondary ion yield, sputter yield, etc.

In particular, for imaging, the use of a He ion beam is of greatadvantage since it may be expected to cause minimal sputtering of thesample when imaging. However, the use of an etching or deposition gaswith the helium ion beam can provide etching or deposition givingzero-damage imaging with ion beam as well as etching and depositionfunctionality. For larger area etching or deposition, the use of heaviergases such as Xe may be expected to deliver more energy to the surfacelayer per ion, hence increasing the yield per ion.

Thus, embodiments provide for optimal choice of ion species fortreatment of a substance. One species may be used for milling, anotherspecies may be used for deposition, another species may be used foretching, and yet another species may be used for imaging. The ability toselect an optimal species for different treatments is a major advantagecompared to using a single species LMIS as in the prior art. Use of aLMIS for milling results in metallic contamination of the specimen. Incontrast, present embodiments enable use of an inert gas for milling.Use of a LMIS for deposition also results in contamination and lowerdeposition rates and further results in undesirable erosion. Incontrast, present embodiments also enable use of an inert gas fordeposition or an organometallic species for direct deposition withoutneed for a precursor gas, resulting in faster deposition rates.

FIG. 1B shows a more detailed diagram of an embodiment of a preferredion plasma source 14. Such a system is described in U.S. patentapplication Ser. No. 10/988,745, published as U.S. Pat. Appl. Publ. No.2005/0183667, entitled “Magnetically enhanced, inductively coupledplasma source for a focused ion beam system” which is incorporatedherein by reference. A coil 1000 is capacitively coupled by impedance210 to an RF source 200. Note that the capacitances shown in FIG. 1B arenominal values that readily can be selected by one of skill in the artaccording to the frequency of operation of the coil, as will bedescribed further below. Coil 1000 is preferably a multi-turn coil thatwraps around a dielectric plasma tube 2000 so that the axis of the coilsubstantially coincides with the axis of chamber 2000 and the beam axis.

When driven by RF source 200, coil 1000 forms a helical RF antenna.Driving the coil with an RF source can impart a time-varying potentialto the plasma, due to capacitive coupling. That is, the coil can producea radial electric field that modulates the plasma. This is undesirablebecause it creates a spread in the beam energy, resulting in chromaticaberration. However, in one embodiment, the antenna is driven at one endby a signal that is out of phase with the signal at the opposite end byas much as 180°. This creates a region interior to the coil where thepotential fluctuations are substantially zero at all times. In thisregion there is substantially no time-varying modulation of the plasmaarising from the time-varying voltage across the coil 1000. Thus, thephase of the antenna can be adjusted to minimize modulation of theionization potential of the plasma in the region where ions areextracted in response to an applied acceleration field. The energy ofthe ions extracted from the plasma, according to this method, issubstantially un-modulated by the RF voltage across the antenna.

However, source 200 does indeed cause electrons to move. Because of theorientation of the coil, free electrons in the plasma circulate aroundthe plasma skin, causing them to collide with atoms to produce ions.This can produce plasma of very high ion density with relatively lowthermal ion energy. A fixed-strength annular magnet about 5 to 10millimeters thick, or a variable-strength electromagnet 3000, thatproduces an axial field strength of nominally 200 to 1000 Gauss may beplaced between an end of the coil and a region 3500 of extraction, andis provided to increase plasma density. The magnet reduces electrondiffusion and loss to the walls of the plasma chamber. Thus, the RFsource is inductively coupled to the plasma and the annular magnetincreases the plasma density in the extraction region.

A split Faraday shield 6000 can be used to screen out the capacitivefield of the coil, but this is less desirable for two main reasons.First, a degree of capacitive coupling is required to ignite the plasma.Using a split Faraday shield usually requires another external powersource (e.g., a Tesla coil) to ignite the plasma. Second, split Faradayshields typically result in some energy loss, due to Eddy currentsinduced in the shield. Without the split Faraday shield, the balancedantenna approach may still result in a sufficient time varying electricfield in areas of the plasma chamber to cause the initial fieldionization required to initiate the plasma.

A beam voltage 400 is electrically connected to a beam energy cap 420,which has an additional low pass filter 410 to ensure negligible RFpick-up to the beam voltage. An extractor voltage source 600, that isnegative with respect to the potential applied to the source electrode4000, is applied to the extraction electrode 4500. Skimmer electrode5000 is at ground potential and provides an aperture through which thedense ion beam passes to produce an ion beam that can be focused withappropriate optics. Thus, the beam is extracted from the extractionregion 3500, with a beam waist formed in the skimmer electrode 5000aperture, and thus propagates along the beam axis in response to anapplied acceleration. Alternatively, beam voltage 400 can beelectrically connected directly to the source electrode 4000 instead ofto the beam energy cap 420.

FIG. 2 shows a circuit of a preferred embodiment, including a plasmaimpedance. Zp, 2010 in parallel with an unknown coil inductancecharacteristic 1010. In series with the parallel combination of theplasma impedance 2010 and coil inductance 1010 is capacitance 8000. Thisparallel-series-parallel combination is in parallel with a secondcapacitance 7000. This series-parallel combination is in series with athird capacitance 210. This entire network is in parallel with the RFsource 200. Clearly, the phase shift across the coil and plasmaimpedance can be controlled by the selection of capacitance values 210,7000 and 8000.

One can therefore select capacitance values 210, 7000, and 8000 toobtain a phase shift across the coil and plasma of 180 degrees. Thus,some embodiments provide a circuit adjustment to achieve a maximumtransfer of power to the plasma, with negligible modulation of theplasma potential, resulting in negligible axial energy spread of theextracted ions.

The embodiment described above minimizes the effects of capacitivecoupling on the ions, leaving only the influence of the pre-sheathpotential gradient. The potential gradient of the pre-sheath region isfinite, but small, and is generally about half the mean electron energy(Te), where Te is only 3 eV for the type of source described above,giving an inescapable lower limit to the axial energy spread (ΔE) of˜1.5 eV.

Embodiments may be conveniently operated at low RF power, nominallyimparting 25 W to the plasma. At this power level a brightness of ˜200Acm⁻²sr⁻¹ can be generated at only

5 keV with an ion current density of 19.6 mA cm⁻². This implies athermal energy of ≦0.15 eV and a plasma density of ˜8×10¹¹ cm⁻³. Pulseplasma densities of 1×10¹⁴ ions cm⁻³ have been attained with thissource, implying that a source brightness of >1×10⁵ A cm⁻² sr⁻¹ isobtainable at a beam energy of 50 keV, with current density of:J_(i)=0.6n_(i)q√{square root over (k_(B)T_(e)/M_(i))}˜2.4 Acm⁻², whereE₀=50 keV, and E_(⊥)=0.15 eV. This yields a beam brightness,

$\beta_{\max} = {\frac{J_{i}E_{0}}{\pi\; E_{\bot}} > {1 \times 10^{5}{Acm}^{- 2}{{sr}^{- 1}.}}}$

Thus, one embodiment is an ion beam system comprising a plurality ofsource gases for which a first and then at least a second gas arecoupled sequentially to a vessel that encloses a region of plasma. Anantenna in proximity to the vessel is excited by an RF electrical sourceto induce ionization of the plasma. Compensation circuitry couples theantenna to the electrical source to substantially reduce oscillations inthe ionized plasma. An extraction mechanism extracts the ionized plasmainto a beam of high current.

FIG. 3 shows an embodiment of a focused ion beam system 101 thatincludes an evacuated envelope 10 in which is located a plasma source 11with an RF antenna with RF supply 33, and impedance matching circuit 27,implemented as described above, to provide a dense plasma for ion beamfocusing column 16. Connected to the plasma source 11 is a bank ofsources 13 to provide different ionizable gases for ionization. Ion beam18 passes from plasma source 11 through column 16 and betweenelectrostatic deflection mechanism 20 toward specimen 22, whichcomprises, for example, a semiconductor device positioned on movable X-Ystage 24 within lower chamber 26.

A turbo-molecular pump 8 is employed for evacuating the source andmaintaining high vacuum in the upper column optics region. The vacuumsystem provides within lower chamber 26 a vacuum of typically betweenapproximately 1×10⁻⁷ Torr (1.3×10⁻⁷ mbar) and 5×10⁻⁴ Torr (6.5×10⁻⁴mbar) with nominally 10 mTorr (1.3×10⁻³ mbar) in the plasma source and<1×10⁻⁶ Torr (1.3×10⁻⁶ mbar) in the column optics chamber.

High voltage power supply 34 may be connected to electrodes of plasmasource 11 as well as to electrodes in focusing column 16 for forming anapproximately 0.1 keV to 50 keV ion beam 18 and directing the samedownward. RF power supply 33 and impedance matching circuit 27 is alsoprovided to energize a coil of plasma ion source 11, as described above.Deflection controller and amplifier 36, operated in accordance with aprescribed pattern provided by pattern generator 38, is coupled todeflection plates 20 whereby beam 18 may be controlled to trace out acorresponding pattern on the upper surface of specimen 22. In somesystems, the deflection plates are placed before the final lens, as iswell known in the art.

The beam from ion plasma source 11 is brought to a focus at specimen 22for either modifying or imaging the surface 22. A charged particlemultiplier 40 used for detecting secondary ion or electron emission forimaging is connected to video circuit 42, the latter supplying drive forvideo monitor 44 also receiving deflection signals from controller 36.The location of charged particle multiplier 40 within lower chamber 26can vary in different embodiments. For example, a preferred chargedparticle multiplier 40 can be coaxial with the ion beam and include ahole for allowing the ion beam to pass. A scanning electron microscope41, along with its power supply and controls 45, are optionally providedwith the FIB system 101.

Signals applied to deflection controller and amplifier 36, cause thefocused ion beam to move within a target area to be imaged or milledaccording to a pattern controlled by pattern generator 38. Emissionsfrom each sample point are collected by charged particle multiplier 40to create an image that is displayed on video monitor 44 by way of videocircuit 42. An operator viewing the image may adjust the voltagesapplied to various optical elements in column 16 to focus the beam andadjust the beam for various aberrations.

Focusing optics in column 16 may comprise mechanisms known in the artfor focusing or methods to be developed in the future. For example, twocylindrically symmetric electrostatic lenses can be implemented toproduce a demagnified image of the round virtual source. Because of thelow axial energy spread in the extracted beam, chromatic blur is minimaland efficient focusing of the beam can be achieved even at lowacceleration voltages (i.e., low beam energies). These properties inconjunction with appropriate focusing optics can be used to generatenanometer, to micrometer scale spot sizes with a range of kineticenergies (about 0.1 keV to about 50 keV) and beam currents.

The realization of very high plasma densities (up to about 1014/cm³),low thermal ion energies (down to about 0.1 eV), low axial energy spread(about 1.5 eV to about 3 eV), the ability to operate with either inertor reactive gases, and the potential for very long life due to minimalerosion of source materials, makes a magnetically enhanced, inductivelycoupled plasma source ideal to be used in conjunction with probe formingFIB optics.

Embodiments can provide beam currents from about a few pico-amperes toabout several micro-amperes. A source brightness of at least about 10⁴A/cm²/sr, up to about 10⁶ A/cm²/sr at about 50 keV can be achieved. Theaxial energy spread is less than about 3 eV and could be as low as about1.5 eV. This contrasts sharply with present day LMISs, which can providea beam brightness on the order of about 106 A/cm²/sr, but with an energyspread on the order of about 5 eV. Also, LMIS sources are generally onlysuitable for generation of beam currents in the picoampere to nanoampererange.

Thus, the plasma sources described above can provide a submicron spotsize with a beam brightness of greater than 10³-10⁵ Acm⁻²sr⁻¹ and anaxial energy spread less than about 1.5-3.0 eV, which makes the plasmasource suitable for micromachining or deposition of submicron features.FIG. 3B shows a graph of performance of both a LMIS and a magneticallyinduced plasma ion source as described herein. The horizontal axis isthe rate of removal of material, in this case silicon. The vertical axisis a measure of the size of the beam. The white curve 302 is shows therate of material removal versus beam size for a Gallium LMIS focused ionbeam. The black curve 304 shows the rate of removal versus beam size fora magnetically induced plasma ion source. The curve 302 lies below thecurve 304 to the left and then rises above the curve 304 to the right.Clearly, in the region where the curve 304 lies below the curve 302, themagnetically induced focused ion beam offers a greater milling rate fora given beam size. With the magnetically induced plasma ion beam, onecan achieve a spot size of less than 200 nanometers with a beam Currentexceeding 50 nano-amperes.

A further advantage of embodiments of the invention is the ability tooperate with any inert gas as well as many reactive gases, (e.g., O₂,N₂, SF₆, etc. . . . ). The ion beam is capable of being focused into abeam diameter of a few nanometers (submicron), up to several tens ofmicrometers. Inert gas beams can readily be generated making embodimentssuitable for applications where gallium or other metallic ion beamsmight be problematic.

FIG. 4 shows a flow chart of an embodiment of a process for milling oretching and deposition using a multi-source, magnetically induced ionbeam system as described herein. First, the system evacuates the chamberthat contains a specimen (element 402). Then, the system introduces afirst ion species such as Xe selected by a user for milling (element404). Note that in one embodiment an etch-enhancing gas, such as XeF₂ orI₂, may be directed to the work piece while directing the first ionspecies to the work piece. The system produces a focused or shaped ionbeam (element 406) and milling is performed using this ion species(element 408). When milling is completed, the system evacuates thechamber (element 410). The system may then introduce a precursor gassuch as tungsten hexacarbonyl (element 412). Then, the user selects asecond ion species such as He to be used for deposition (element 414).The system produces a focused ion beam (element 416) and performsdeposition, with the helium ions providing energy to dissociate thetungsten hexacarbonyl to deposit tungsten on the specimen (element 418).If another specimen is to be treated, (element 420), the process beginsanew (element 402). Otherwise, the process ends (element 422). Note thatin a different process deposition may be performed followed by etching.

Embodiments also provide for deposition of a metal using an ionized gascontaining metal atoms For example, tungsten may be deposited byionizing tungsten hexacarbonyl. Ionization of this gas results inrelatively fast tungsten deposition compared to depositing to tungstenthrough a gas injection system and then causing bombardment by an ionbeam to cause vibrations which disassociate the tungsten from thecarbon, leaving the tungsten on the surface.

Thus, one embodiment of an ion beam system for treatment of a specimencomprises an organometallic gas coupled to a plasma chamber. A helicalantenna is positioned around the plasma chamber and excited to ionizethe organometallic gas within the plasma chamber. Circuitry in a networkcomprising the antenna impedance matches a source of excitation to theantenna. An extraction mechanism extracts an ionized organometallic beamfor deposition of the metal of the beam onto a specimen.

FIG. 5 shows a flow chart of an embodiment for milling followed bydeposition using an organometallic ion species. First, the systemevacuates the chamber that contains a specimen (element 502). Then, thesystem introduces a first ion species selected by a user for milling(element 504). The system produces a focused ion beam (element 506) andmilling is performed using this ion species (element 508). When millingis completed, the system evacuates the chamber (element 510). Then theuser selects an organometallic ion species such as tungsten hexacarbonylto be used for deposition (element 514). In another embodiment, C₆₀ maybe employed for depositing a resistive layer on the specimen. Thus, astep of introducing a precursor gas may be omitted. The system producesa focused organometallic ion beam (element 516) and performs directdeposition upon the specimen (element 518). If another specimen is to betreated, (element 520), the process begins anew (element 502).Otherwise, the process ends (element 522).

As another example, the invention can be used for “circuit edit,” inwhich an integrated circuit is modified in a series of steps. Forexample, a buried conductor may be exposed by milling a hole in thecircuit using a focused ion beam of inert ions and an etch-enhancing gas(either in the beam or introduced separately) that preferentially etchesoxides to expose. The buried conductor may be severed using a focusedbeam of inert ions and an etch-enhancing gas that is selective for metaletching. The hole is then filled using by ion beam deposition of aninsulator, for example, using an inert ion and TEOS as the precursorgas.

In another example of circuit edit, two buried conductors may be exposedas described above, and then the conductors can be connected using ionbeam deposition of a metal using an inert ion and an organometallicprecursor gas. If necessary, an insulating layer can be deposited tocover any conductors on the surface before the holes are milled.

Although the present invention and some of its advantages have beendescribed in detail, it should be understood that various changes,substitutions and alterations can be made herein without departing fromthe spirit and scope of the invention as defined by the appended claims.For example, while most embodiments are described using a focused ionbeam, the term should be understood to include a shaped ion beam.Because the invention can be used in different applications fordifferent purposes, not every embodiment falling within the scope of theattached claims will achieve every objective. Moreover, the scope of thepresent application is not intended to be limited to the particularembodiments of the process, machine, manufacture, composition of matter,means, methods and steps described in the specification. As one ofordinary skill in the art will readily appreciate from the disclosure ofthe present invention, processes, machines, manufacture, compositions ofmatter, means, methods, or steps, presently existing or later to bedeveloped that perform substantially the same function or achievesubstantially the same result as the corresponding embodiments describedherein may be utilized according to the present invention. Accordingly,the appended claims are intended to include within their scope suchprocesses, machines, manufacture, compositions of matter, means,methods, or steps.

1. A method of charged particle beam processing, comprising: providingan ion beam system having a first gas supply and a second gas supply,the first and second gas supplies being selectively connected to theplasma chamber of an ion source for producing ions of a first type orions of a second type, respectively, the ion beam system includingfocusing optics for forming a beam of ions extracted from the plasmachamber; selectively causing a gas from the first gas supply to enterthe plasma chamber; and processing a work piece using a beam of ions ofthe first type extracted from the plasma chamber; selectively causing agas from the second gas supply to enter the plasma chamber; processingthe work piece using a beam of ions of the second type extracted fromthe plasma chamber, in which the work piece is not removed from thevacuum chamber and the vacuum chamber is not exposed to atmospherebetween processing the work piece using the beam of ions of a first typeand processing the work piece using the beam of ions of a second type.2. The method of claim 1 in which the ion source comprises a RF-excited,impedance matched plasma chamber for receiving an ion species andextracting an ion beam from the plasma chamber.
 3. The method of claim 2in which the impedance matched plasma chamber is coupled to impedancematching circuitry that is adjustable to vary an amount of powertransferred to the plasma for a particular selected ion species.
 4. Themethod of claim 1 in which processing a work piece using a beam of ionsof the first type includes directing a beam having a submicron spot sizetoward the work piece and in which processing a work piece using a beamof ions of the second type includes locally directing a beam having asubmicron spot size toward the work piece.
 5. The method of claim 1 inwhich processing a work piece using a beam of ions of the first typeincludes processing the work piece using a Gaussian shaped ion beam. 6.The method of claim 1 in which processing a work piece using a beam ofions of a first type or processing a work piece using a beam of ions ofa second type includes processing the work piece by one of the followingprocesses: depositing material using ion beam induced deposition ordirect material deposition; removing material using ion beam sputteringor chemically-enhanced ion beam etching; forming an image of the workpiece using ion beam imaging; or analyzing the composition of the workpiece using secondary ion mass spectroscopy.
 7. The method of claim 1 inwhich processing a work piece using a beam of ions of a first type orprocessing a work piece using a beam of ions of a second type includesdirecting a beam of inert ions or a beam of reactive ions at the workpiece.
 8. The method of claim 1 in which processing a work piece using abeam of ions of the first type or processing a work piece using a beamof ions of the second type includes directing a beam of ions to deposita material on the work piece surface.
 9. The method of claim 8 in whichdirecting a beam of ions to deposit a material on the work piece surfaceincludes directing a beam of ions that include atoms other than those tobe deposited and that decompose to deposit the atoms of the desireddeposit material.
 10. The method of claim 8 in which directing a beam ofions to deposit a material on the work piece surface includes directinga beam of ions that include atoms only of the material to be deposited.11. The method of claim 1 in which processing a work piece using a beamof ions of a first type includes directing a beam comprising ions of atleast two chemical compositions or in which locally processing a workpiece using a beam of ions of a second type includes directing a beamcomprising ions of at least two chemical compositions.
 12. The method ofclaim 1 in which processing a work piece using a beam of ions of a firsttype or processing a work piece using a beam of ions of a second typeincludes directing a gas toward the work piece from a gas injectionsystem, the gas comprising a precursor gas that decomposes in thepresence of the ion beam to deposit a material onto the work piecesurface or an etch-enhancing gas that reacts in the presence of the ionbeam to remove material from the surface.
 13. An ion beam system,comprising: a plurality of source gas connections for connectingmultiple source gases to a vessel that encloses a region of plasma; avessel enclosing the region of plasma; an antenna in proximity to thevessel, the antenna excited by an RF electrical source to induceionization of the plasma; circuitry that couples the antenna to theelectrical source to substantially reduce oscillations in the ionizedplasma; and an extraction mechanism to extract the ionized plasma into abeam.
 14. The system of claim 13, further comprising charged particlebeam optics for focusing the beam into a Gaussian shape.
 15. The systemof claim 13, wherein the source gas connections selectively couples asource of an inert gas or a source of a reactive gas to the plasmachamber.
 16. The system of claim 13, wherein the source gas connectionsselectively couples to the vessel a first gas used for deposition and asecond gas used for etching.
 17. The system of claim 13, wherein a gascoupled to the vessel comprises a source that decomposes on the workpiece surface to deposit a material or a gas that combined with thematerial on the surface to form a volatile reaction product, therebyetching the surface, or that forms a non-volatile reaction product thatremains on the surface.
 18. The system of claim 13, wherein the systemexhibits an energy spread that is less than about 4 eV.
 19. The systemof claim 13, further comprising a focusing mechanism that produces abeam of high brightness exceeding 1000 A/cm²/sr.
 20. The system of claim13, wherein an extracted beam exhibits an extracted beam energy of about8 keV or greater.
 21. The system of claim 13, wherein an extracted beamexhibits a current exceeding about 50 nano-amperes and is focused to aspot size of less than 200 nanometers.
 22. The system of claim 13,wherein the beam formed from a selected gas is focused to a submicronspot size.
 23. An ion beam system for treatment of a specimen,comprising: an organometallic gas coupled to a plasma chamber; a plasmachamber to which the organometallic gas is coupled; a helical antennapositioned around the plasma chamber and excited to ionize theorganometallic gas within the plasma chamber; circuitry in a networkcomprising the antenna to impedance-match a source of excitation to theantenna; and an extraction mechanism for extracting an ionizedorganometallic beam for deposition of the metal of the beam onto aspecimen.
 24. The system of claim 23, wherein the circuitry comprises acapacitance in series with a parallel combination of a capacitance andthe helical antenna.
 25. The system of claim 23, wherein theorganometallic gas is tungsten hexacarbonyl.
 26. The system of claim 23,wherein the beam is focused to a submicron spot size.
 27. A method forproducing an ion beam, comprising: providing a plurality of differentgas sources to be individually and sequentially selected to be coupledto a plasma chamber; providing circuitry coupled to an antenna to reducemodulation of a plasma potential; selectively coupling to the plasmachamber a first one of the plurality of different gases and then atleast a second one of the plurality of gases; applying RF power to anantenna that couples energy to the selected gas within the chamber toinduce ionization of a gas to produce an ion plasma; and extracting anionized beam from a region of extraction in proximity to the antenna.28. The method of claim 27, wherein one selected gas is used for etchingand another selected gas is used for deposition.
 29. The method of claim27, wherein the circuitry is adjustable to vary an amount of powertransferred to the plasma for a particular selected gas.